This invention relates to a two cycle engine and more particularly to a two cycle engine construction that will improve the running performance of the engine.
As is well known, two cycle engines operating with direct cylinder injection tend to have a very lean mixture in the combustion chamber at the time of ignition when under light and mid-range loads and this can cause high combustion temperatures which result in the formation of large amounts of NOX in the exhaust gases and also the likelihood of knocking. This problem is particularly prevalent in connection with diesel engines. In order to preclude these problems, an arrangement has been provided for throttling the intake air flow or the air flowing through the scavenge passage under light load conditions. This can be conveniently done by providing a throttle valve in the intake passage that serves the crankcase chambers and which will restrict the air flow under low load and low speed conditions.
Although the aforedescribed type of construction is effective in limiting the amount of NOX emissions and also reducing the likelihood of knocking, it gives rise to another problem. In a two cycle engine during the time when the scavenge port is opened, there can be a time when the pressure in the crankcase chamber is negative when intake air throttling is employed. If this occurs, then the exhaust gases can flow back through the scavenge passage to the crankcase chamber giving rise to further problems.
It is, therefore, a principal object to this invention to provide a two cycle crankcase compression engine operating in way so as to avoid NOX emissions and knocking while at the same time preclude the flow of exhaust gases back into the crankcase chambers.
It is a further object to this invention to provide an arrangement for operating a two cycle crankcase compression engine so as to reduce NOX emissions, knocking and other poor running, particularly at low speed conditions.
The aforenoted objectives can be met by providing a balance passage that interconnects the crankcase chambers of the engine and which has valving which is opened at low and mid range speeds so as to reduce the amount of scavenging in the engine without causing backflow of exhaust gases from the combustion chamber to the crankcase chamber through the scavenge port. When this is done, however, if the balance passage is positioned so that it is below the crankcase chamber or if any portions of the interconnecting passageways have downwardly inclined portions, then any lubricant or fuel which tends to condense in the crankcase chambers may flow back into this balance passage system with obvious disadvantages.
It is, therefore, a still further object to this invention to provide an improved balance system interconnecting plural crankcase chambers of a two cycle engine and in which the system is configured so that lubricant or fuel cannot collect in the balance system.